The present invention is concerned with a method of influencing the motion of a weft yarn which has to be drawn off a stock bobbin and runs towards a weft insertion mechanism of a loom, and in particular a projectile loom, At any given time in a weaving cycle the weft yarn is transferred for a weft insertion to a weft insertion member which passes through the shed, where the weft yarn is additionally accelerated at any given time by a compressed-air nozzle arranged between the stock bobbin and the weft insertion mechanism, and after the weft insertion is drawn back by a predetermined length by a deflector element movable transversely to the direction of weft insertion and deflected locally from a yarn path running essentially stretched into a yarn path cranked like a loop, and upon a following weft insertion is returned from the latter at any given time towards the yarn path running stretched.
The invention is further concerned with a loom for the performance of the above-described method.
EP-A-0 155 432 discloses a loom which contains between the stock bobbin and the deflector element a nozzle arrangement with a compressed-air nozzle for accelerating and a compressed-air nozzle for braking the weft yarn which is being fed to the weft insertion mechanism, as well as a compressed-air nozzle arranged between the deflector element and the weft insertion mechanism for transferring the weft yarn to the insertion member. The nozzle intended for accelerating the weft yarn in the known arrangement is acted upon by compressed air during the greater part of the weft insertion process in order to avoid the weft yarn being drawn off by the insertion member alone. Towards the end of the weft insertion process when the insertion member arrives at the catching side of the loom, the feed of compressed air to this accelerator nozzle is shut off and the braking nozzle acting in the opposite direction is acted upon by compressed air. The yarn transfer nozzle is activated each time only before the weft insertion in order to introduce the end of the weft yarn which has to be gripped into the insertion member. An accelerator nozzle which is active during essentially the whole weft insertion period demands a relatively elaborate arrangement and control of the compressed-air supply and consumes a relatively large amount of compressed air. In the case of looms of high weft insertion power, when a loop-shaped length of weft yarn is being returned towards the stretch position, in particular upon stretching out the portion of weft yarn being steadily accelerated by the accelerator nozzle and the weft insertion member, a "snatch" may additionally occur which, when handling sensitive yarn material, e.g., wool, may lead to weft yarn breakage.